1. Field of the Invention
The present invention relates to a method for testing the reliability of telephone systems, and more particularly to a reliability testing method which is based upon orthogonal arrays and customer field data.
2. Description of the Relevant Art
Modern telephones are software controlled devices that are used in many different environments, such as call centers, investment banking firms, law firms, etc. The same telephone device is typically not used in the same way in different environments. In other words, an investment banker does not use a telephone in the same way that an operator in a call center uses the same telephone. Moreover, each telephone can be in a different state depending upon a particular call being initiated or received. For example, a telephone can be involved in a point-to-point (“p2p”) call or a conference call, or it can be on hold, or it can be transferred from one caller to another, or it can be idle, etc. Additionally, the state of the telephone can vary depending upon whether the telephone is being used to initiate a call or whether it is being used to receive a call. When all the possible states for an individual telephone device are considered, it is possible that a telephone can literally be placed in millions of different states.
Since a telephone can be placed in so many different states, it is very likely that some of these states may cause the telephone to lock up or fail due to a software programming error. When a software controlled telephone locks up, it can usually be reset by disconnecting the telephone from the network, thereby removing electrical power from the telephone. If the failure or lock up is caused by the telephone being moved into a particular state, it is important to discover which state caused the failure and to correct the software.
In the prior art, reliability tests for software controlled telephone systems are usually based upon random test generation (operational profiles), but these random tests do not guarantee that “good” or “effective” combinations of test parameters are chosen. Hence, the prior art reliability tests do not yield a fast solution that converges to a mean-time-to-failure solution with a given confidence factor. It is known in the prior art to use orthogonal arrays for testing, however, the orthogonal arrays of the prior art only provide all pair-wise combinations of test parameters, which are typically used to replace exhaustive system tests. For example, these orthogonal array techniques may be based on the so-called Taguchi method, which can reduce the number of combinations of test parameters. But the selection of the test parameters are typically arbitrary and do not reflect realistic system usage in a particular environment. For example, financial institutions where there are many long conference calls versus call switch centers where there are many short calls that are transferred to other numbers are some examples of different operational environments for telephones.
An example of the Taguchi method is described in U.S. Pat. No. 6,604,092, by Steward, entitled, “Expert system utilizing a knowledge base and design of experiment (DOE) techniques”. Although the Taguchi method is a powerful tool for testing software and other systems, the use of the Taguchi method and orthogonal matrices alone cannot provide an acceptable solution for the reliability testing of telephone systems, because a telephone has too many possible states that vary widely from one environment to the next. There are simply too many combinations of test parameters to effectively test the telephone for reliability in each environment in which it is expected to be used.